The invention relates generally to advanced propulsion technologies and more particularly to control systems for microwave electrothermal thrusters.
Launches of small and miniaturized satellites such as CubeSat are occuring more and more frequently. A CubeSat is made of up multiples of 10×10×10 cm cubic units that have a mass of no more than 1.33 kg per unit. Because of their small size, propulsion systems that rely on large portions of a space vehicle's size, weight, and power allowances are not suitable for this market. Solid rockets, for example, are less efficient and lack an ability to relight. Chemical rockets have complex plumbing and delicate components, which are generally not suited for small missions. Cold-gas thrusters are inefficient and do not provide enough change in velocity (delta-V) for extended missions. Hall-effect thrusters (HET) require large power levels whle arcjets have electrodes in the flow path of the propellant that can erode.
Advanced propulsion technologies, such as electric propulsion, are commonly used for station keeping on commercial communications satellites and for primary propulsion on some scientific missions because they have significantly higher values of specific impulse (Isp). Station-keeping refers to maneuvers that are taken by an object in orbit to maintain the orbit or its relative position to one or more other orbiting objects. For example, small impulses from the propulsion system are used for precise positioning of spacecraft relative to each other, such as a space telescope that is formation flying with an occulting disk for a planet finding mission.
A microwave electrothermal thruster (MET) uses microwave energy to heat up a gaseous propellent to convert it into plasma. The plasma expands within a resonate cavity in the MET. As the pressure increases, the plasma is expelled through a nozzle, creating thrust. Previously developed versions of microwave propulsion have relied upon one of two methods for introducing the microwave energy to the propellant: 1) beaming the microwaves from ground stations to the flying propulsion system, or 2) use of an onboard klystron, magnetron, or traveling wave tube amplifier (TWTA) connected to the thrust chamber. These solutions do not meet the size, weight and power limitations of small and miniturized satellites. Generally, these other solutions are incredibly inefficient and not worth the cost to implement.
Thus, there is a need for an improved MET having a small packaging volume and mass. There is a further need for a MET control system that provides high values of specific impulse (Isp) with low power requirements and precise and automatic control.